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Recently purchased a great 1984 18' Outrage without power with t-top. Minimum recommended is 70 hp 25" shaft. Had a recently purchased leftover 2004 4-stroke Yamaha 50 hp High Thrust with a 21" shaft. Decided to give it a chance since it was sitting around and after spending some time calculating Whaler hull forms, weights, and expected top speeds with different hps. With a black stainless 13 1/2 x 14 prop and full 64 gallons of fuel the boats performance far exceeds my expectations. Quick to get up on plane and easily cruises at 22 mph a bit over half throttle, top end is close to 30. The slightly longer High Thrust shaft on the T50TLR, larger gearcase with lower gearing and larger diameter prop seem to get the necessary bite in the water and only get some cavitation if sharply turning without lowering power setting. Added benefit of the shorter shaft is reduced drag and draft. After getting my tach installed and do some actual rpm/speed/mpg calculations will share that information if ya'll are interested.
22mph cruise with a 50 hp four stroke on an 18 Whaler? That really surprises me. I would have sworn it would not be enough. Good for you for giving it a shot, I guess the adage you don't know until you try certainly applies here.
I can't see how this boat would even get up on plane with a 20 inch shaft motor when it is designed for a 25 inch shaft. Single motors should be 25 inch shaft length and twin motors should be 20 inch shaft length. http://www.whalercentral.com/readarti...icle_id=35
Does not compute with my testing. Like to hear more.
Joe...the 21" shaft measurement can be found in the download of the owner's manual. Actual length of many outboards routinely vary by plus or minus up to one inch. While rigging the boat in my driveway several of my nautical naysayer neighbors had similar concerns as yours about the too short shaft. Remember that the High Thrust prop is 2" larger in diameter than standard F50, geared lower and weighs in at only 250 lbs. Part of my research prior to rigging was to look at Yamaha performance bulletins and seeing the T50TLR pushing 22' pontoons to 20 mph and some planning hulls up to 30 mph.
